Method for volume determination and geometric reconstruction

ABSTRACT

A method for determining a volume of ablated tissue includes the steps of supplying energy to tissue, indicating an axis within the tissue, and simulating slicing of the tissue substantially perpendicular to the axis to obtain a plurality of simulated slices. Each of the plurality of simulated slices has a thickness, a cross-sectional perimeter, and a trajectory point defined by the axis within the tissue. The method further includes the steps of determining a volume of each of the plurality of simulated slices based on the trajectory point, the cross-sectional perimeter, and the thickness of each simulated slice, and summing the volumes from each of the plurality of simulated slices to obtain the volume of the ablated tissue.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/260,811 filed on Oct. 29, 2008, which claims priority to U.S.Provisional Patent Application No. 60/984,605 filed on Nov. 1, 2007, theentire contents of each of which are incorporated herein by reference.

BACKGROUND

1. Technical Field

The present disclosure relates to electrosurgical apparatuses, systemsand methods. More particularly, the present disclosure is directed to asystem and method for determining the volume of an ablation lesionduring and/or after a tissue ablation procedure utilizingelectrosurgical electrodes and imaging means.

2. Background of Related Art

Energy-based tissue treatment is well known in the art. Various types ofenergy (e.g., electrical, ultrasonic, microwave, cryo, heat, laser,etc.) are applied to tissue to achieve a desired result. Electrosurgeryinvolves application of high radio frequency electrical current to asurgical site to cut, ablate, coagulate or seal tissue. In monopolarelectrosurgery, a source or active electrode delivers radio frequencyenergy from the electrosurgical generator to the tissue and a returnelectrode carries the current back to the generator. In monopolarelectrosurgery, the source electrode is typically part of the surgicalinstrument held by the surgeon and applied to the tissue to be treated.A patient return electrode is placed remotely from the active electrodeto carry the current back to the generator.

In the case of tissue ablation, high radio frequency electrical currentis applied to a targeted tissue site to create an ablation volume. Theresulting ablation volume may then be observed and various ablationmetrics may be measured and recorded. Conventional methods of obtainingablation metrics include recording the small diameter, large diameter,and height of the ablated tissue to calculate the volume. Typically,these three parameters are input for the equation for ellipsoidal volumeto calculate an approximate ablation volume. Conventional methods suchas this often provide inexact measurements, inconsistent recordings, aswell as inaccurate reporting of achieved volumes. Further, conventionalmethods of volumetric calculation lack evaluative tools such asdetermining the effect of adjacent structures on the ablation volume,qualifying the completeness of the ablation volume, predicting specificvolumes and/or shapes based on a given energy applicator configuration.

SUMMARY

The present disclosure elates to a method for determining a volume ofablated tissue. In a first step, energy is supplied to tissue. In asecond step, an axis within the tissue is indicated. In a third step, asimulated slicing of the tissue substantially perpendicular to the axisis performed to obtain a plurality of simulated slices. Each of theplurality of simulated slices has a thickness, a cross-sectionalperimeter, and a trajectory point that is defined by the axis. In afourth step, a volume of each of the plurality of simulated slices isdetermined based on the trajectory point, the cross-sectional perimeter,and the thickness of each simulated slice. In a fifth step, the volumesfrom each of the plurality of simulated slices are summed to obtain thevolume of the ablated tissue.

According to another embodiment of the present disclosure, anelectrosurgical system includes an electrosurgical generator coupled toone or more electrodes configured to be inserted into a portion oftissue. The electrode(s) is further configured to supply electrosurgicalenergy to the portion of tissue to create an ablation volume. The systemfurther includes a feedback unit coupled to an imager for imaging theportion of tissue to obtain a graphical scan of the ablation volume andthe electrode(s). A controller marks an axis of the electrodes withinthe graphical scan. The controller is further configured to simulateslicing the graphical scan substantially perpendicular to the axis toobtain a plurality of simulated slices. Each of the plurality ofsimulated slices has a thickness, a cross-sectional perimeter, and atrajectory point defined by the axis of the electrode(s). The controlleris further configured to determine a volume of each of the plurality ofsimulated slices based on the trajectory point, the cross-sectionalperimeter, and the thickness of each simulated slice and further, to sumthe volumes from each of the plurality of simulated slices to determinethe ablation volume.

According to yet another embodiment the present disclosure, a method ofstoring a library of ablation data related to the use of a treatmentdevice includes a first step of providing a treatment device having aparticular configuration. In a second step, electrosurgical energy issupplied to the treatment device for application to tissue to generate aplurality of feedback parameters based on the particular configurationof the treatment device. In a third step, an imaging device is providedfor imaging tissue to create one or more images corresponding to theplurality of feedback parameters based on the particular configurationof the treatment device. The imaging device is configured to communicatewith a feedback unit for storing the library of ablation data. In afourth step, the image(s) and the plurality of feedback parameters arestored in the library of ablation data for subsequent retrieval. Theimage(s) and the plurality of feedback parameters correspond to theparticular configuration of the treatment device applied to tissue. In afifth step, a completeness factor is determined based on deviationsbetween the image(s) corresponding to feedback parameters based on theparticular configuration of the treatment device and ablation datastored in the library corresponding to feedback parameters generated byapplication to tissue of a treatment device having substantially thesame configuration.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present disclosure are described herein withreference to the drawings wherein:

FIG. 1A shows an electrosurgical system for tissue ablation, measuringablation volume, and displaying image scan data according to oneembodiment of the present disclosure;

FIG. 1B shows an electrode defining a path through tissue for heatingablation according to one embodiment of the present disclosure;

FIG. 1C shows a sliced segment of the tissue of FIG. 1B;

FIG. 2 illustrates a method for determining an ablation volume accordingto embodiments of the present disclosure; and

FIG. 3 shows an electrosurgical system for tissue ablation, measuringablation volume, and displaying image scan data according to anotherembodiment of the present disclosure.

DETAILED DESCRIPTION

Particular embodiments of the present disclosure are describedhereinbelow with reference to the accompanying drawings. In thefollowing description, well-known functions or constructions are notdescribed in detail to avoid obscuring the present disclosure inunnecessary detail.

The present disclosure provides for a system and method for determininga volume of an ablation lesion and providing a geometric reconstructionof the ablation volume. The ablation lesion may be created by applyingany suitable energy, such as radiofrequency (“RF”), microwave,electrical, ultrasound, heat, cryogenic, and laser. For the purposes ofillustration, the following description assumes the application of RFenergy to create ablation lesions in accordance with embodiments of thepresent disclosure.

Referring to FIG. 1A, an ablation electrode 100 is shown having aninsulated shaft 102 and an electrically exposed tip 103. Electrode 100may be, for example, a high frequency or RI thermo-ablation electrodeconfigured to be placed in the body of a patient (not explicitly shown)so that the tip 103 is near a target volume, such as a cancerous tumoror other tissue structure within the body. A hub or junction connectorelement illustrated schematically by 106 may be any type of connectiondevice such as jacks, hoses, ports, etc. that connect the RF electrodeto a power source, such as a radiofrequency (RF) generator 107. Thegenerator 107 according to an embodiment of the present disclosure canperform monopolar and bipolar electrosurgical procedures, includingtissue ablation procedures. The generator may include a plurality ofoutputs for interfacing with various electrosurgical instruments (e.g.,a monopolar active electrode, return electrode, bipolar electrosurgicalforceps, footswitch, etc.). Further, the generator includes suitableelectronic circuitry configured for generating radio frequency powerspecifically suited for various electrosurgical modes (e.g., cutting,blending, division, etc.) and procedures (e.g., monopolar, bipolar,vessel sealing, tissue ablation).

Also shown is a control system 109 coupled to generator 107, which maybe a computer, a microprocessor, or an electromechanical deviceconfigured to receive RF energy input parameters from RF generator 107,such as power, current, voltage, energy, time, impedance, etc. In someembodiments, a coolant supply system (not explicitly shown) may also beincluded, for example, in operative cooperation with RF generator 107and/or incorporated within RF generator 107. The coolant supply systemis configured to output various feedback parameters such as temperature,multiple temperatures at different points, and the like into the controlsystem 109. The coolant supply system parameters can then be used asfeedback control input parameters. Based on one or more of theseparameters, the control system 109 modulates, moderates, or otherwisemonitors output response at the generator 107.

Also shown in FIG. 1 is a computer system 111, which may be, forexample, a PC or computer graphic workstation. The computer system 111is coupled to the control system 109. Computer system 111 processes theparameters of the RF generator 107 and coolant supply system (notexplicitly shown) plus other geometric parameters regarding theelectrode as well as image scan data taken before, during or afterthermo-surgery. Computer system 111 assimilates all of these parametersand displays them in various representations, digital representations,and analog meter type representations, as an interface to the operatoror controller of the processor during the preplan process or during theprocess of ablation heating itself. In one embodiment, image data 120might represent image scan data from such image scanners such as fromCT, MRI, PET, or other tomographic or X-ray, plain film, or digitizedimage scan data. That data may be stored in the computer system 111 andbe represented as an array of raw data, slices, reconstructed slices,three-dimensional renderings, “slice and dice” three-dimensional ortwo-dimensional renderings, contoured or segmented anatomicalstructures, color rendered, differentiated structures, both pathologicaland normal so that the surgeon may substantially visualize the anatomyand pathology of the patient prior to, during, or after the procedure.Data from CT or MRI may be taken days or even months prior, and could beput into stereotactic or non-stereotactic space, for example, byutilizing any suitable imaging software and/or image processing softwarein conjunction with one or more graphic references or other suitablemarking systems or software.

Image data 121 may represent ultrasound scan data or sonic monitoringdata such as from a sonic detector system that can visualize before,during, and after the thermo-surgery procedure the course of theelectrode in the body, electrode position with respect to anatomy, andeven the process of the heating mechanism and result thereof. This datacould also be fed into computer system 111 and represented in variousways alternatively on a graphics display screen. Image data 121 may bestored in computer system 111 to correspond with particularconfigurations of electrode 100, such as, for example, geometricparameters of the electrode tip 103. In this manner, a library offeedback data may be stored in computer system 111 and indexed accordingto particular configurations of the electrode, thereby assisting thesurgeon in predicting future ablation results for a given electrodeconfiguration. Further, there may be calculation algorithms, look-uptables, heuristic algorithms, historical clinical data, etc. that can beused in a preplan setting and displayed, implemented, overlaid, and usedto control the image data, course of RF generator output, as well as thecontrol system to tailor or preplan the results of the ablation that canbe visualized again on the computer system 111 and further computed andstored therein.

Computer system 111 includes a display 115 for outputting image data 120and 121, such as the real-time or preplanned trajectory of a probe path126 and electrode tip as the tip 126 is inserted into the body and/or atumor structure represented by a cloud of dots 125. This might also be,for example, the display from an ultrasonic, CT, or MRI scanner thatactually visualizes the probe 126 and a tumor 125 or a profused volumecorresponding to the destructive ablation volume, perhaps represented orvisualizable as volume 125. Use of CT contrast agents or dyes can beused to mark the ablation volume following ablation, and this can give adirect view of the results immediately following the heating process.

Display 115 may also be configured to show a preplanned path of anelectrode in a particular slice or reconstructed slice plane ofvolumetric rendering in a three-dimensional aspect (not explicitlyshown), and also configured to show isotherm surfaces or intersectedsurfaces or isotherm lines (not explicitly shown), which might representa preplan or a calculation of the ablation volume around the tip of theelectrode. Display 115 may also be configured to show a view, slice, orreconstructed slice, and within it a preplanned or actual plan orpost-thermosurgery path representing the approach of a thermosurgicalprobe 100 into the patient's anatomy to achieve a target volume thatmight be seen on that image slice such as for example a tumor as seen onimage data 120 and 121.

Volumetric calculations for ablation volumes may be determined fromcross-sectional perimeters of slices of a target tissue site and/orblock of tissue and subsequently reconstructed and graphicallyrepresented in a 2-D and/or 3-D manner on display 115, as will bediscussed in further detail below.

Turning now to FIG. 1B, a trajectory or path 131 of electrode 100through ablation volume 125 is shown. Path 131 may also be defined as anaxis of electrode 100 through ablation volume 125. Electrode 100 is usedto create an ablation lesion at a targeted site such as volume 125 byheating tissue via application of RF energy from the generator 107 tothe tissue. Path 131 of electrode 100 through volume 125 provides atrajectory reference or point 135 from which volumetric calculations maybe made for volume 125, as will be discussed in further detail below.Volume 125 may be deconstructed into a plurality of slices, depictedhere as 125 a, 125 b, 125 c, and 125 d, for enabling volumetricdetermination of volume 125 and, further, graphical representation indisplay 115, FIG. 1C shows a cross-sectional view of any slice 125 n ofthe plurality of slices 125 a-d indicated by line 1C-1C in FIG. 1B. Eachof the plurality of slices 125 n defines a cross-sectional perimeter 140n generally concentric about trajectory point 135 n.

In one embodiment of the present disclosure, the reconstructed graphicalrepresentation is fitted to a specific geometry (e.g., ellipsoidal,spherical, etc.) for viewing on display 115. For example, Euclideandistances between perimeter 140 of volume 125 and the perimeter of apre-specified geometry may be minimized to fit volume 125 to thepre-specified geometry. In this manner, valuable feedback may beprovided to a surgeon on the consistency and/or the predictability ofthe ablation volume achieved based on given energy applicatorconfigurations (e.g., electrode size, electrode tip geometry, etc.). Thegraphical representation of the reconstructed ablation also allows thesurgeon to qualify the completeness or a completeness factor of theablation lesion achieved based on geometrical similarity between thelesion and any one or more of a particular preplanned geometry provided,for example, by the control system 109. The graphical representation ofthe reconstructed ablation may also be used to determine the impact fromadjacent structures such as, for example, other electrodes, lungs,bones, vessels, tissue extraneous to the present procedure, etc. on agiven ablation, as will be discussed in further detail below.

A method for volumetric determination of an ablation volume forsubsequent geometric reconstruction and graphical representationaccording to embodiments of the present disclosure will now be describedwith reference to FIG. 2 in conjunction with FIGS. 1B and 1C.

In step 300, electrosurgical energy is supplied from the RF generator107 to the electrode 100. As illustrated in FIG. 1B, electrode 100 isused to create an ablation lesion by heating volume 125 via applicationof RF energy from the generator 107 to volume 125.

In step 310, path or trajectory 131 of electrode 100 through a targetsite such as, for example, volume 125 (FIG. 1B) is indicated. Path 131of electrode 100 through volume 125 defines trajectory point 135therethrough relative to perimeter 140 of tissue block 125. Trajectorypoint 135 may be substantially defined through the center of mass oftissue block 125. Trajectory 131 and/or trajectory point 135 may bemarked with CT contrast agents or dyes following ablation, giving adirect view of the results immediately following the heating process.

In step 320, volume 125 is cut or “sliced” substantially perpendicularto trajectory point 135 into a plurality of slices 125 a-d. Slices 125a-d may be obtained via an image scanner such as, for example, CT, MRI,PET, or other tomographic or X-ray, plain film, or digitized image scandata for subsequent 2D or 3D graphical representation. In this manner;various dimensions and/or measurements of each of the plurality slices125 a-d may be indicated such as, for example, thicknesses, volume,cross-sectional perimeter, etc. for each of the plurality of slices.

In step 330, a thickness, indicated in FIG. 1B as A, and across-sectional perimeter 140 a-d for each of the plurality of slices125 a-d is determined. Cross-sectional perimeters 140 a-d for each ofthe plurality of slices 125 a-d may be derived, for example, from scandata 121 in the computer system 111 such as post-ablation MR images thatmay or may not include CT contrast agent. Other embodiments of thepresent disclosure may include deriving from a measurement taken usingconventional means such as, for example, dial calipers, slide calipers,digital calipers, electronic calipers, or the like.

In step 340, the volume of each of the plurality of slices 125 a-d isdetermined. Any suitable method for determining volume may be used suchas, for example, the contour or perimeter method. This method utilizeseach slice of volumetric data individually and models the shape of thevolume as defined on each slice. For example, cross sectional perimeter140 a-d for each slice 125 a-d may be used to determine the volume usingsuch method. Alternatively, for each slice 125 n, thickness A may bemultiplied by the perimeter area of that particular slice to determinethe slice volume. This determination is carried out for each of theplurality of slices 125 a-d.

In step 350, the volume determinations derived in step 340 for each ofthe plurality of slices 125 a-d are summed to yield an ablation volume.In this manner, an accurate volumetric determination is made rather thanapproximated calculations yielded by conventional and/or presentlycompeting volumetric calculation methods.

Referring now to FIG. 3 in conjunction with FIGS. 1B, 1C, and 2, apatient's body is represented schematically by element P, and there is atarget volume represented by the dashed line 301. A thermosurgery probe302 is inserted into the patient's body such that the tip of the probe303 is placed within the target volume 301. Attached to or inconjunction with or cooperatively coupled with the probe (or probes) 302is an imaging device 311 which, when placed against the surface of thepatient's skin or an organ within the patient's body, images a portionof the patient's body P, including the probe 302 and the target volume301 or the environment around these elements.

The radiofrequency, laser, high frequency, or other power generator isrepresented by 304, and in the case of a high frequency generator, areference electrode 305 is attached to the patient's body around theshoulder region is shown in FIG. 3. The reference electrode 305 might bea gel pad, large area, conductive pad or other type of standardreference electrode that is used in electrosurgery. The imaging device311 is connected to a monitoring circuit or controller system 360 thatcan be used to image, analyze, filter, and monitor the image scan dataor the like which is received from the imaging device 311. This system360 may also involve a power source and processor for the imaging device311. The system 360 includes a feedback unit 309 configured to controlmonitoring, preplanning, and/or imaging of an ablation area. Feedbackunit 309 includes at least one display 315 and/or 325 configured tographically display 2D or 3D image data. For example, in display 315there may be represented in 2D or 3D slice or volume representations,image scan data taken from an image scanner such as CT, MR, PET, orultrasound prior to, during, or after the thermal ablation. In thisinstance, a patient's skin 317 is defined, a target volume (e.g., tumor316) is shown, and in the dashed line is a preplanned probe path 318 fora thermal ablation high frequency electrode (e.g., probe 326). By meansof such visualization, the probe path 318 can be manipulated within theimage or image stack of CT or MR slices, and an optimal path forplacement can be achieved. This path could be achieved by criterion fromthe surgeon such as bringing the probe path along a principal axis ofthe tumor 316 or from a direction that avoids some critical structuressuch as arteries, lung, optic nerve, neural structures, etc. Thus, basedon image scan data taken from the imaging device 311 prior to thethermal ablation, the surgeon can do a preplanned study and decide onthe optimal positioning of the probe 326.

On the display 325 is shown a real-time representation of the probe 326as it is inserted into the patient's body. The margin 327 may be areconstruction, either theoretical or actual, of the result of the RFheat ablation. For example, if the window represents an ultrasonicreconstruction, this could be a theoretically generated graphicrepresentation within a preplanned ultrasonic slice direction and probedirection to show what the ecogenic or ultrasonic image would look likewhen particular cooled tip RF, generator parameters are invoked or used.This window may alternatively represent real-time image data from the CTor MR or other type of scanning means, if the patient is within such ascanner during the RF heating process. The window may also represent thechanges or modifications or digitally subtracted differential changes ofthe tissue volume as a result, directly or indirectly, of the ablationisotherms. Thus, one may visualize directly the effect of heating on thepatients tissue, and this may be displayed in such a window. There maybe a superposition of a preplanned or prescanned tumor volume, ascompared to the actual volume of the tumor at the time of surgery or theablation volume as one detects it during surgery.

Direct detection of changes in the physiology as a result of the heatingto gauge the extent of the ablation volume can be done by ultrasound,CT, MRI, PET, and other imaging modalities, and can be displayed on thedisplay 325 of the feedback unit 309 or, indeed, on the graphics displayof the ultrasound or CT, MR, or other scanning machine as supplied bystandard manufacturers. Each of these scanning devices has a graphicsdisplay on a CRT, liquid crystal, or other means which can display theresults of the tomographic or volumetric scanning. These can be used inconjugation with the thermosurgery to evaluate the effect of thethermosurgery itself. Use of ultrasound and standard sonic detection andscanning may be used in conjugation with the thermosurgery to evaluatethe effect of the lesion or ablation process.

The entire process of the heating could be preplanned by the operatorhours or days before based on the imaging and preplanned calculations ofablation volume with the tip geometry and ablation parameters describedwith respect to FIG. 1. Thus, system 360 could basically mediate theentire process of supply of RF power from generator 304. Indwellingcontrollers, electronics, microprocessors, or software may be programmedto govern the entire process or allow preplan parameters by the operatorbased on his selection of a tip geometry and overall ablation volume asselected according to a tumor or pathological volume to be destroyed.Many variants or interconnections of the block diagram shown in FIG. 3or additions of said diagram could be devised by those skilled in theart of regulation systems.

While several embodiments of the disclosure have been shown in thedrawings and/or discussed herein, it is not intended that the disclosurebe limited thereto, as it is intended that the disclosure be as broad inscope as the art will allow and that the specification be read likewise.Therefore, the above description should not be construed as limiting,but merely as exemplifications of particular embodiments. Those skilledin the art will envision other modifications within the scope and spiritof the claims appended hereto.

What is claimed is:
 1. A method for determining a volume of ablatedtissue, comprising: providing electrosurgical energy to tissue via anablation device to create an ablated tissue volume; generating atrajectory of the ablation device through the ablated tissue volume;generating a plurality of image slices of the ablated tissue volumetransverse to the trajectory; determining, for each of the plurality ofimage slices of the ablated tissue volume, a surface area of the imageslice based on the trajectory of the ablation device relative to across-sectional perimeter of the image slice; determining, for each ofthe plurality of image slices of the ablated tissue volume, a volume ofthe image slice based on the determined surface area of the image sliceand a thickness of the image slice; and summing the determined volumesof the image slices to determine a volume of the ablated tissue volume.2. The method according to claim 1, further comprising indicating atrajectory point through the ablated tissue volume based on thetrajectory of the ablation device.
 3. A method for determining a volumeof ablated tissue, comprising: providing electrosurgical energy totissue via an ablation device to create an ablated tissue volume;imaging the ablated tissue volume to generate a plurality of imageslices of the ablated tissue volume; determining, for each of theplurality of image slices of the ablated tissue volume, a surface areaof the image slice based on a trajectory of the ablation device relativeto a cross-sectional perimeter of the image slice; determining, for eachof the plurality of image slices of the ablated tissue volume, a volumeof the image slice based on the determined surface area of the imageslice; and summing the determined volumes of the plurality of imageslices to determine a volume of the ablated tissue volume.
 4. The methodaccording to claim 3, wherein the determined volume for each of theplurality of image slices is based on the determined surface area of theimage slice and a thickness of the image slice.
 5. A method fordetermining a volume of ablated tissue comprising: providingelectrosurgical energy to tissue via an ablation device to create anablated tissue volume; imaging the ablated tissue volume transverse to atrajectory of the ablation device through the ablated tissue volume togenerate a plurality of image slices of the ablated tissue volume;determining, for each of the plurality of image slices of the ablatedtissue volume, a surface area of the image slice based on the trajectoryof the ablation device; determining, for each of the plurality of imageslices of the ablated tissue volume, a volume of the image slice basedon the determined surface area of the image slice; and summing thedetermined volumes from each of the plurality of image slices to obtainthe volume of the ablated tissue volume.
 6. The method according toclaim 5, wherein the determined surface area for each of the pluralityof image slices is based on the trajectory of the ablation devicerelative to a cross-sectional perimeter of the image slice.
 7. Themethod according to claim 5, wherein the determined volume for each ofthe plurality of image slices is based on the determined surface area ofthe image slice and a thickness of the image slice.